Antenna Comparisons

In the course of trying to choose the optimal antenna we always find ourselves comparing manufacturer's specifications about gain, which are all too often sparse or expressed in inconsistant units of measure.  Or worse, relying only on marketing bullets claiming  "best deep fringe".

An alternative approach is to simply compare measured signal levels of one antenna to another.  If we do this on a number of different antennas, let's call 'em A, B, C, and D, and we find that A is better than B, and B is better than C, then it follows that A is also better than C.

So the links below provide antenna comparisons of relative field performance of a few popular VHF and UHF antennas.  That is, various pairs of antennas are compared to each other.  This comparison of relative antenna performance removes numerous variables that otherwise make it almost impossible to use comparisons of gain specifications.  What was different about the antenna range at which the measurements were made?  How accurately were all losses of baluns, cables, etc., taken into account?  How carefully was the measurement equipment calibrated?  What units were the cited gain numbers expressed in (dBd or dBi)?

- All measurements of antenna pairs are made back to back, as quickly as possible, in order to minimize the error contribution from time variant environmental conditions.
 - The receive transmission path consists of about 12 feet of Belden 7916A RG6 as down lead, a Kitz Technologies (1dB NF) amplifier whose gain I've measured to be 20dB and flat as a pancake across the combined VHF/UHF spectrum, followed by another 8 feet of RG6 to the spectrum analyzer.
- In all cases, antennas were tested with their stock baluns, whether built in or supplied as a 300 to 75 ohm matching transformer.
- Height was about 15' above ground level.
- From measurement to measurement, the antenna under test was rotated to produce maximum amplitude across all channels within the bandwidth segment (not necessarily maximum channel flatness of any one channel).
- Also from one antenna comparison to another the vertical scale of the analyzer may change; e.g., 10 dB / division or 5 dB / division.

In other words, a lot of care was taken to insure that the predominant variable between comparisons was the antenna itself.

Antennas Direct 91XG vs Winegard PR9032  Channel Master CM-4228 vs Antennas Direct DB8
Antennas Direct 91XG vs their New DB8 Channel Master CM-4228 vs Winegard HD-8800
Antennas Direct DB8 vs Winegard HD-8800 New Channel Master CM-4228 vs Old CM-4228
New DB8 vs Old DB8 Channel Master CM-4228 vs SuperQuad
Y10-7-13 vs new Antennas Direct C5 Winegard HD7698P vs Y10-7-13 and PR9032
8-Bay Shootout  - CM-4228 vs DB8 vs HD-8800 8-Bay Shootout  -  Revisited for VHF !

A Few Notes About The Measurements
The following notes attempt to clarify the measurement environment, conditions, and definitions.
  • Nothing here should be interpreted as attempting to represent antenna "performance"; the only parameter being compared here is received signal level, a function of an antenna's sensitivity, or gain.  In practice there are numerous other factors that affect performance; height above ground, reflections that can cause multipath, the quality (and thus loss) of downlead cable, poor house distribution, splitters, amplifier quality, installation anomolies, and so on.
  • None of the captures are intended to present actual (absolute) field strength or gain.  Rather, each result is presented as a comparison between two antennas or configurations, at an identical field location.
  • Every effort was made to insure the only variable was the unit under test.  Antennas were raised at exactly the same spot, were located at exactly the same height (with one qualifier as follows), were carefully positioned, the same cables, amplifier, etc. were used, and the elapsed time between measurements was minimized as much as humanly possible.  The qualifer is that when comparing units of significantly different vertical dimensions, such as a Yagi to an N-Bay, the height chosen on the mast was the lower of the maximum acheivable heights of the vertical centers of the two designs.  To clarify, if the maximum attainable height of the vertical center of an 8-Bay was 14" below the top of the mast, the vertical center of a compared Yagi would also be located at 14" below the top of mast (ignoring the possibility that the Yagi could have been raised another foot).  Nevertheless, all of these physical aspects represent possible sources of error.
  • The Spectrum Analyzer being used is an 80's vintage HP8590B.  It has an 75 Ohm impedance option, whose calibration is out of date, and which has some irritating frequency drift over time.  This occasionally causes traces to not line up precisely across the horizontal axis.  However, observations of indicated level while monitoring independent signal generators show very little gain drift; i.e., the gain seems stable over time.  Again, for these relative measurements, accurate determination of the absolute level or frequency is unimportant.  The important factor is difference in observed levels (e.g. the level from one antenna relative to the other), and the internal gain of the instrument does not significantly change over the typically 15 minutes between antenna measurements.
  • The measurements are made at the coordinates 39 21 14.63 N 120 5' 19.54" W.  The terrain is extremely mountaineous and rugged.  Note that while TVFool predictions serve well in LOS scenarios, at these coordinates they're really more of a hint at reality; are not generally as good as RFProfiler, and neither tool is highly precise for this 1Edge and 2Edge, rugged mountain terrain location.
  • Channels available at the measurement location include VHF channels 7, 9, 13, and UHF 23 and 26 at a compass heading of 103 degrees (East by South East), and UHF 15, 20, 24, 30, 33, 44, 47, 51, and 55 at a heading of about 28 degrees (North East).  [Note: following the June 2009 cutover 9 moved down 8.  Thus some VHF comparisons may show different channels].
  • Almost all signals are fairly weak in the area, with the exceptions of VHF 7, 8/9, 13 and UHF 44, and suffer from multipath distortion due to mountainous terrain.  But to arrive purely at a conclusion about relative received signal strength between two antennas, signal quality (flatness) is a "don't care".  E.g., it doesn't matter that a given channel has nulls (dips) or peaks across its approximately 6MHz channel bandwidth.  The only thing being measured here is the relative receive level of one antenna compared to another.
  • Where the channels 23, 24, and 26 are involved in the comparisons, side lobe response can yield differences in receive levels that are dramatic.  Take care as you study comparisons of these channels to take into account that 23 and 26 are about 75 degrees to 24.  It means that while looking at captures including channels 23 and/or 26, for example, anything observed for 24 is irrelevant.
  • In all pictures, the images of the separate screen captures of two antennas are merged.  The Green color is the antenna judged to be the overall better performer.  The pictures have 96dpi resolution and if you have a scroll wheel on your mouse you can scroll up/down to zoom in/out on them.
  • At the time some of the earliest measurements were performed UHF Channel 23 was not on the air, and UHF Channel 55 was.  After the June 2009 DTV cutover this reversed; e.g., 23 came on the air and 55 went off.
  • At different points in time different vertical scale values were used.  In earlier measurements 10 dB per division was used, and thus each minor division represents 2 dB.  But in later measurements 5 dB per major division was used, and thus each minor division is 1 dB.  So you may have to squint a little bit on some.  The indication of scale appears at the top left of each capture, as something like "LOG 10dB/" indicating 10 dB / division.
  • The "REF" (vertical axix reference level) also varies somewhat arbitrarily.  It is irrelevant.  What ever value was convenient for the channels being observed was used, and care was taken to insure that absolutely the same level was used for both antennas being compared.